Merged Netgen 4.3.1: a Delaunay/Frontal 2D/3D mesh generator.

Thanks a lot to Nicolas Tardieu for this!

- mesh.algo -> algo2d and algo3d
- replaced most of the remaining radio buttons with Fl_Choices (requires
  less screen real estate)

create the default project file in the home directory if no "current"
directory is defined (e.g. when double-clicking on the icon on Windows/MacOS)

removed old unused options

- generalized vertex array class to use reallocatable arrays

- introduced vertex arrays in post for all triangles: this speeds
  things up tremendously for ALL scalar views: 2d scalar views of
  course, but also for 3d isos (tets, hexas, etc.) and all smooth
  normals. The costly computations (compute the isos, get the normals)
  are only done ONCE each time the view is changed. Then we just pass
  the vertex array to OpenGL everytime we need to redraw (e.g. when we
  rotate the scene)

- removed the display list code alltogether: it's completely blown
  away by the new vertex array code!

for the record: with the new drawing code, you can

- rotate 500,000 triangles in real time on a 3-year old linux PC
(tested with a boing 747 surface mesh from CU: 10 times faster than
old code)

- display and rotate in real time 10 transparent+smooth shaded 3D isos
for a 1 million tet mesh (about 1 frame per second with the new code;
took tens of seconds with the old one)

Awesome :-)

removed unused geom.overlay option

removed unused geom.highlight option + small cleanup of the selection code

add 1 more verbosity level; bump default to 3

- removed context.default_plugin

- changed the main so that we load the plugins *before* we set the
  options (this way you can save your favourite plugin options in
  .gmsh-options, too)

doc -convert

"gmsh -convert file file" now also translates meshes into the newest
format (in addition to parsed->binary post-processing views)

better progname

introduced GMSH_EXTRA_VERSION so that we can differentiate official/unofficial
releases

More "airplane" work...

- rewrote the way we handle lights: glEnable(GL_LIGHTING) is now used
  at the lowest level, where it belongs. This fixes many lighting
  glitches, and should make the whole stuff much more predictable;

- simplified the display modes for geometry and mesh: the choice
  between wireframe/solid is now independent of the choice of
  lighting/no lighting (and there is a new "Enable lighting" option
  for the geometry, too--even if it does only affect things like
  normals/tangents at the moment);

- brand new code to draw really nice (shaded) 3D arrows + 3 options
  that fully parameterize them (they can degenerate into pyramids,
  cones, w/ or w/o stems, etc.);

- new options so that we can also use the new arrows outside the
  post-processing module (e.g. for tangents/normals).

- "alt+d" now simply switches between solid and wireframe mode;

- new shortcut "alt+w" to switch the lighting mode for all the modules
  (geo/mesh + all post views) at once.

Update copyright notice

better -convert

Added "append" argument to WriteView (so that "gmsh -convert file file"
can handle all the views in the input file and not only the first one).

Following a discussion with Laurent, we can now combine multiple views
(under certain conditions) into multi time step ones. This permits e.g.
to output separate .pos files for each time step, and still have a real
time evolution in gmsh. Pretty neat :-)

New post-processing range mode to adapt the scale for each time step (i.e.,
min/max is time step dependent)

Cleaned up the whole Include/Merge/Open mess (removed the ugly
yyin/yyname tables in the parser, made the Merge routine reentrant
+ uniformized all the INFO/STATUS messages).

This should fix a nasty side effect from this morning's
commit (wrong yynames when doing multiple merges in the same
file).

Prepare for commercial release

Save the chosen FLTK theme in the per-session resources

Fix a couple of bugs for 2nd order elements. Seems to work OK for 2D
meshes now. 3D is still kinda flaky, and extrusion is not implemented.

- add PNG check in Get_BuildOptions()
- move "make doc" to top-level Makefile
- better "make purge"

Corrections apres relecture / part 1

Added shortcuts.texi

Fix whitespace in copyright headers

pretty print build options

pretty print build options

Make headers self-contained

add progname in -info

GPL -> General Public License

License stuff

Indented all source files using utils/gmshindent

Add some indent directives

Clean up VERSION_FLAGS and OS_FLAGS (use HAVE_FLTK instead of _FLTK,
remove _BLACKBOX, etc.)

Updated copyright

Introduce OpenGL display lists for drawing meshes. Does not seem to
work much faster on my machine, though.